EP2010363A1

EP2010363A1 - Method of producing a fibrous layer for the manufacture of a preform of a composite part

Info

Publication number: EP2010363A1
Application number: EP07731940A
Authority: EP
Inventors: Joëlle Lalande; Frédéric Ballion; Dirk Feltin
Original assignee: SNECMA Propulsion Solide SA
Current assignee: Safran Ceramics SA
Priority date: 2006-04-26
Filing date: 2007-04-25
Publication date: 2009-01-07
Anticipated expiration: 2027-04-25
Also published as: UA92638C2; US8034273B2; EP2010363B1; JP5155301B2; FR2900420A1; FR2900420B1; JP2009534236A; RU2425748C2; US20090098331A1; WO2007125249A1; DE602007007072D1; RU2008141871A

Abstract

The invention relates to a method of producing a fibrous layer intended to form a preform of an axisymmetric composite part having a non-developable surface, characterized in that it comprises the steps consisting in: defining an annular space (23) with a first and second fabric (20, 21) respectively delimiting an internal periphery and an external periphery; arranging fibres between the fabrics (20, 21) by placing the fibres in the annular space in at least one direction and by holding said fibres on the fabrics by stitching; performing circular connection stitching in the vicinity of the internal periphery of the annular space (23); and cutting the fibrous layer thus formed in the annular space (23) in order to extract it from the fabrics.

Description

Process for producing a fibrous stratum for manufacturing a composite part yne preform

Background of the invention

The invention relates to the production of fibrous layers for the manufacture of fiber preforms for composite parts comprising a fibrous reinforcement and having a shape of revolution and non-developable surface such as ring surfaces or truncated sphere.

A particular field of application of the invention is the production of fibrous reinforcements used for the manufacture of composite reinforcements of flexible abutments. Flexible stops are commonly used in the field of propulsion to form joints connecting a nozzle to the body of a thruster. These stops are formed by alternating rigid composite armatures having a sphere ring shape with layers of elastically deformable material such as an elastomer.

One method currently used to form such composite reinforcement is to drape and mold layers of carbon fabric preimpregnated with a resin (eg an epoxy resin). More specifically, the method comprises the following steps: cutting, in a fabric of carbon fibers or pre-impregnated glass, strata in the form of annular sectors having an approximate developed form of truncated cone, draping layers of preimpregnated fabric according to a pattern in a rosette on a male mold having a spherical ring-shaped surface corresponding to the inner surface of the spherical reinforcement to be made, compacting the strata under vacuum by means of a membrane, setting up a female mold having a surface in the form of a spherical ring corresponding to the external surface of the reinforcement to be produced, - press curing of the assembly, and demolding of the reinforcement. This gives a rigid piece with fiber reinforcement for better resistance to mechanical stress.

However, the above method is very difficult to implement.

The draping of fiber layers to form the fibrous reinforcement is a manual operation that takes place directly on a shaping support and that does not allow precise control of the orientation and the amount of fibers at any point of the reinforcement . The placement of the female mold can lead to slippage of the layers and fold formation.

This technique does not offer, therefore, a good reproducibility between the parts which can then have different mechanical characteristics, in particular vis-à-vis the fiber content and their orientation.

In the case of a laminated flexible abutment, it is important that all the armatures of the abutment have similar shapes and mechanical characteristics for good behavior of the abutment.

Furthermore, the layers are formed with pre-impregnated fibers which have less flexibility than dry fibers, which makes it even more difficult to conform the strata to the shape of a piece of non-developable revolution. There are of course other types of composite parts (eg engine casing) which have forms of revolution and non-developable surface and which comprise a fiber reinforcement whose fibers are oriented according to the mechanical forces so as to increase mechanical resistance of the workpiece. However, as for the flexible abutment reinforcement, there is no method for systematically producing fibrous layers having a constant fiber quantity and orientation for forming fibrous reinforcements having non-rotational shapes. developable with homogeneous geometric characteristics. In addition, certain types of parts also need to be reinforced locally. For this purpose, the fibrous reinforcement must have at certain locations larger fiber thicknesses. The production of fibrous layers with portions of fibers that are thicker and able to deform to fit non-developable forms of revolution becomes even more difficult, particularly with regard to the control of the orientation of the fibers and the level of reproducibility between the layers.

Object and brief description of the invention

The present invention aims to overcome the disadvantages of the processes of the prior art by providing a method for producing fibrous layers capable of forming preforms or fibrous reinforcements having forms of revolution and non-developable surface and in which the quantity and the orientation of the fibers can be accurately and reproducibly controlled.

This object is achieved by means of a process for producing a fibrous stratum for forming a preform for a piece of revolution and a non-developable surface, the method comprising the steps of:

defining an annular space with a first and a second canvas delimiting respectively an inner periphery and an outer periphery,

arranging the fibers between the scrims by placing the fibers in the annular space in at least one direction and holding said fibers on the scrims by stitching,

- Making a circular connection seam in the vicinity of the inner periphery of the annular space, and

- Cut the fibrous layer thus formed in the annular space to extrude the scrims.

With the method of the invention, the fibrous layer for forming a preform having a non-developable surface revolution shape is made flat between two scrims. Therefore, the orientation of the fibers can be precisely controlled and allow the production of parts particularly well suited to the mechanical stresses to which they must be subjected. The fibrous stratum according to the invention is preferably made using an automatic embroidery machine. to place the fibers between the two scrims. Thus, it is possible to automate the placement of the fibers and to form identical fibrous layers, particularly as regards the orientation and the quantity of the fibers used. According to one aspect of the invention, additional fibers are added to fill the free spaces present between the fibers arranged between the two scrims, the additional fibers being attached to the adjacent fibers by stitching. This ensures a constant fiber rate over the entire fibrous layer to obtain preforms or fibrous reinforcements having homogeneous geometric characteristics.

The fibers used may in particular be carbon fibers or glass fibers.

The present invention also relates to a method of manufacturing a fibrous reinforcement for a flexible abutment reinforcement comprising the formation of a preform alternating at least two fibrous layers, in which process the first ply is made in accordance with the method of producing a fibrous stratum for forming a non-developable surface revolution part described above. The second layer is formed by placing on the first layer, maintained in shape on a spherical tool, a layer of fibers oriented perpendicularly to the fibers of the first layer.

Thus, the fibrous stratum manufacturing method of the invention allows the manufacture of a fibrous reinforcement for a flexible abutment reinforcement particularly well adapted to the mechanical requirements required for the reinforcement. Indeed, the armature must have good resistance in two perpendicular directions, one corresponding to the axis of the armature and the other perpendicular to this axis. For this purpose, reinforcement of the reinforcement is formed by alternating layers whose fibers are oriented successively in one or other of these two directions. With the method of the invention, the most difficult layer to achieve, namely the stratum whose fibers are oriented according to the reinforcement axis, can be carried out flat between the two canvases, which allows to control the orientation and the quantity of fibers in a precise and reproducible manner for each stratum and to obtain a homogeneous fibrous reinforcement adapted to the mechanical stresses. The stratum thus produced can be easily put in place on a spherical tool while retaining the orientation of the fibers. It is then possible to produce a dry fiber reinforcement (without pre-impregnated fibers) which already has the form of the reinforcement to be produced, namely a form of revolution having a non-developable surface. According to one aspect of the invention, the second layer is made by filamentary winding on the first layer.

Once the fibrous reinforcement has been produced, it is placed in a mold in which a thermosetting resin is injected under pressure, the polymerization of the resin then being carried out by heat treatment. A rigid composite reinforcement is thus obtained which comprises a fibrous reinforcement structurally adapted to withstand the mechanical stresses to be experienced by the reinforcement and which has a virtually non-existent porosity. The subject of the invention is also a process for manufacturing a flexible abutment consisting in forming a laminated structure comprising a plurality of rigid composite reinforcement interposed with layers of elastically deformable material, each reinforcement being produced in accordance with the method of manufacturing a reinforcement previously described.

In a particular aspect, the flexible stop manufacturing method comprises the steps of:

- Making several fibrous reinforcements of increasing size according to the method described above, - maintaining the reinforcements in each other with spacers between each armature, said spacers defining the thickness of the layers of elastically deformable material,

injecting under pressure into the reinforcements a thermosetting resin, applying a heat treatment to polymerize the resin in each reinforcement so as to form a plurality of rigid composite reinforcement,

- remove the tabs, and

injecting or casting an elastic material into the spaces present between the rigid composite reinforcement to form layers of elastic material between them.

This implementation of the method makes it possible to perform the injection and the polymerization of the resin simultaneously in the fibrous reinforcements and then proceed to the formation of the layers of elastic material between each reinforcement thus formed. The present invention furthermore relates to a method of manufacturing a composite part of the housing type comprising the formation of a fibrous reinforcement or preform composed of at least one fiber stratum which is produced in accordance with the method for producing a fibrous layer intended to form a preform of revolution piece and non-developable surface described above. The fiber stratum is formed of fibers oriented in two different directions.

According to one aspect of the invention, one or more epaissssssment portions are formed at specific locations on each stratum of fibers, said portions being made by repeating the placement of fibers at locations determined on the stratum. Thus, it is possible to manufacture parts with local reinforcements which are directly made on the fibrous layer and which can easily control the thickness and orientation of the fibers, and in a reproducible manner for each stratum.

Brief description of the drawings

Other features and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the appended drawings, in which; FIG. 1 is a schematic sectional view of a rear part of a thruster equipped with a flexible abutment; FIG. 2 is a schematic view from above showing the production of a fibrous layer according to an embodiment of FIG. FIG. 3 is an enlarged perspective view of a portion (item III) of FIG. 2 showing the placement and sewing of fibers by an automatic embroidery machine; FIG. 4 is an enlarged view of a part (item IV) of the stratum of FIG. 2 on which the placement and sewing of additional fibers is performed by an automatic embroidery machine,

FIG. 5 is a half-sectional view, according to the reference V, of the fibrous layer of FIG. 2 showing the realization of a circular seam, FIG. 6 is a half sectional view, according to the V mark, of the fibrous layer of FIG. 1 showing the removal of the stratum from the scrim,

FIG. 7 is a schematic view from above showing the fibrous layer of FIG. 2 after adding additional fibers and removing the scrims,

FIG. 8 is a schematic perspective view of a forming tool used for the manufacture of a fibrous reinforcement according to one embodiment of the invention, FIG. 9 is a schematic perspective view of the tooling. FIG. 8 is a diagrammatic detail view showing the positioning of pin bars in the tool of FIG. 9, FIG. 11 is a diagrammatic perspective view of FIG. a filament winding installation,

FIG. 12 is a schematic perspective view of the tool of FIG. 9 further comprising, on the fibrous stratum, a filamentary winding stratum; FIG. 13 shows a fibrous reinforcement formed of a superposition of layers alternating strata; FIG. 14A is a perspective view showing the assembly used for the injection of resin into a fibrous reinforcement, FIG. 14B is a partial schematic sectional view showing the fibrous reinforcement of FIG. 7 and the filament winding strata. injection of resin into a fibrous reinforcement,

FIG. 15 is a photograph illustrating an exemplary embodiment of a composite flexible stop reinforcement in accordance with the invention; FIG. 16 is a top view showing the placement of fibers in two distinct orientations in accordance with another embodiment; of the invention, Figs. 17A, 17B, 18A, 18B and 19 are schematic views showing the production of a fibrous stratum having fibers in two distinct orientations according to another embodiment of the invention, Figure 20 is a schematic perspective view of a fibrous layer comprising portions of reinforcements in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The fibrous layer forming method of the present invention can be used generally for the manufacture of any type of part preform having a shape of revolution and whose surface is not developable.

As explained in detail below, this method makes it possible initially to produce on canvas a flat fibrous layer which can subsequently adapt to the shape of the piece of revolution and non-developable surface. This layer can be used alone or be part of a stack of several layers to form the preform or fibrous reinforcement of the part to be manufactured.

In a first example of implementation, the method of the invention is used in the manufacture of composite flexible stop frames. As illustrated in FIG. 1, it is common to articulate a nozzle 11 of a thruster or rocket motor 10 by means of a flexible abutment 12 comprising a laminated structure constituted by an alternation of layers of elastically deformable material 121 ( for example elastomer) and rigid composite reinforcements 122 having a truncated sphere shape. The stop 12 thus forms a flexible connection between the nozzle 11 and the body 13 of the thruster so that the nozzle can be oriented by means of a jack 14 disposed between the body 13 of the thruster and the diverging portion 15.

The manufacture of the reinforcement consists first of all in producing a fibrous reinforcement consisting of a stack alternating layers having fibers oriented in a first direction corresponding to the axis of the reinforcement and called "strata at 0 °" with strata in a second direction perpendicular to the axis of the reinforcement and to the strata fibers at 0 ° and called "90 ° strata".

The fibers used to make the layers may in particular be glass or carbon fibers depending on the performance and costs sought. The layers at 0 ° are réaϋsées according to the method of the invention. As illustrated in FIG. 2, the realization of a stratum at 0 ° is made from two canvases 20 and 21 defining an annular space

23. The scrims 20 and 21 define respectively the inner and outer periphery of the annular space whose width | is chosen slightly larger than the necessary dimensions for the stratum at 0 °.

Fibers 22 are arranged radially between the two scrims so as to best fill the annular space. The fibers 22 are arranged using the TFP ("Tailored Fiber Placement") placement technology. This technology involves placing and securing fibers at specific locations on a support (scrim) using an automatic embroidery machine.

However, in the present invention, the TFP technology is used in a different way. Indeed, as described for example in document US 2004/0074589, the TFP technology is used to place and sew fibers on a support which is an integral part of the stratum. In a different way, in the present invention, supports (canvases) are used solely to define the shape and dimensions of the fibrous stratum to be produced. The supports are not found in the final fibrous layer. If one uses the usual TFP technology, the fibrous layer embroidered on the support has too much rigidity and can not be deformed to fit a three-dimensional shape of revolution and non-developable surface.

More specifically, and as illustrated in FIG. 3, the machine delivers the fibers from a reel (not shown) containing, for example, rovings (or "rovings") of glass and positions them by means of a guide 25 in the 23. To maintain the fibers thus placed, the machine comprises a sewing head 24 which sews the fibers at their ends on the scrims 20 and 21 with a very fine thread 26, for example polyethylene or polyester. The placement and sewing of the fibers is programmed into the numerical control of the machine.

Due to the annular shape of the space 23 and the radial placement of the fibers therein, spaces remain between the fibers placed by the machine which are larger as the periphery is approached. outer ring space. To maintain an identical fiber content at any point of the stratum, fibers are added 27 In this case, the automatic embroidery machine is programmed to fill the free spaces between the fibers 22 by placing the additional fibers 27 in these spaces and in the spaces between the fibers 22 as shown in FIG. sewing them to the adjacent fibers.

Once all the spaces have been filled, the annular space 23 is filled by a layer 30 containing a constant fiber content at all points. A circular seam 31 (FIG. 5) is then produced in the vicinity of the inner periphery of the annular space in order to maintain the fibers before removal of the fibrous stratum 30 from the scrims, which can be produced, for example, by cutting the stratum 30 along the inner and outer peripheries of the annular space 23 using cutting tools 28 and 29 (eg knives, electric scalpels, pressurized water jets, lasers, etc.) (Figure 6). Figure 7 shows the fibrous layer 30 after removal of the scrims.

A fibrous layer is thus obtained, the fibers 32 of which are held together by the circular seam 31 while maintaining a high degree of flexibility which makes it easy to conform to a shaping tool. FIG. 8 illustrates an example of such a tool that can be used to produce an alternating stack of layers at 0 ° and at 90 °. The tool 40 has a hemispherical shape with slots 41 to allow the passage of pins for the realization of the strata at 90 °. FIG. 9 shows the fibrous stratum 30 when it is positioned (ie shaping) on the tool 40. Since the fibers 32 are relatively free on the outer periphery side of the stratum 30, the stratum 30 adapts perfectly to the the spherical shape of the tool 40. Then is positioned in each slot 41 of the tooling a bar 42 of pin support 43 (Figure 10). A stratum 50 at 90 ° is made directly on the 0 ° layer consisting of the fibrous layer 30 by filament winding (Figure 11). For this purpose, the top 42 of the tool 40 is fixed on a mandrel 61 of a winding machine 60, In this way, the machine 60 drives the tool 40 in rotation while continuously delivering a thread 57 by means of a grommet 62 mounted on an arm 63 which is shifted as winding takes place so as to form successive loops on the stratum 30 maintained between the barbs 43. The wire 57 is preferably made of the same material (eg glass or carbon fibers) as that comprising the fibers 32 of the fibrous layer 30.

When the winding is complete, the fibrous stratum at 0 ° is completely covered by a stratum 50 at 90 ° (FIG. 12), that is to say a stratum whose fibers 52 are oriented perpendicularly to the fibers 32 of the stratum. underlying 30.

The fibrous reinforcement or the preform of the flexible abutment reinforcement is thus produced by alternating on the tool 40 fibrous strata 30 at 0 ° with strata 50 to 90 ° made by winding. Each stratum at 0 ° is carried out according to the method described above, possibly increasing each time slightly the width of the layer 30 to account for the increase in volume in the stack.

By way of example, for a reinforcement with a thickness of 3 mm having a fiber content by volume of 50%, the following stacking is carried out: one ply at 0 ° by TFP placement with a thickness of 0.35 mm, 1 stratum at 90 ° by filament winding with a thickness of 0.53 mm, - 1 stratum at 0 ° by TFP placement with a thickness of 0.35 mm, - 1 stratum at 90 ° by filament winding with a thickness of 0.53 mm, - stratum at 0 ° by TFP placement with a thickness of 0.35 mm,

1 stratum at 90 ° by filament winding with a thickness of 0.53 mm, 0 ° stratum at 0 ° by TFP placement with a thickness of 0.35 mm, Once the stacking is completed (FIG. 13), it is possible to a fibrous reinforcement 80 composed of dry fibers oriented alternately in two perpendicular directions corresponding here in the direction of the mechanical stresses to which the stopper will be subjected.

The strata at 0 ° and 90 ° present in the stack can be bonded to them via wires 64 passing through the layers in the direction of their thickness (Z direction) (FIG. 13). These inter-layer bonds can be made by using the slots 41 of the tooling as a seam passage for the threads 64. The threads 64 can be for example PET (polyethylene terephthalate) or carbon.

The part is then molded by impregnating the reinforcement 80 with a thermosetting resin which is polymerized by heat treatment. To this end, the well-known RTM ("Resin Transfer Molding") transfer molding process is used. According to the RTM method, the fibrous reinforcement 80 is placed between a mold 70 and a counter-mold 71 (FIG. 14A), the reinforcement being first positioned on the mold 70. Once assembled together (FIG. 14B), the mold 70 and the counter-mold 71 define an internal space 72 comprising the reinforcement 80 and in which a thermosetting resin 73 is injected via a feed orifice 710 formed on the lower part of the counter-mold 71. The counter mold 71 comprises in addition to orifices 711 which are connected to exhaust ducts 712 maintained under pressure. This configuration allows the establishment of a pressure gradient between the lower part of the reinforcement where the resin is injected and the upper part of the reinforcement located near the orifices 711. In this way, the thermosetting resin 73 injected substantially at the level of the lower part of the reinforcement 80 will progressively impregnate the entire reinforcement circulating in the space 72 to the orifices 711 through which the surplus is removed.

The resin used can be, for example, a temperature class epoxy resin 180 ⁰ C (maximum temperature supported without loss of characteristics). Suitable resins for RTM methods are well known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of the temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the workpiece must be subjected. Once the resin is injected into the entire reinforcement, it is polymerized by heat treatment in accordance with the RTM method. After the injection and the polymerization, the part is demolded. It can optionally undergo a post-baking cycle to improve its thermomechanical characteristics (increase of the glass transition temperature), such as for example a cycle of 2 hours at 180 ^° C. Finally, the piece is cut away to remove the excess of resin and chamfers are machined. No other machining is necessary since, the part being molded, it respects the required dimensions.

As illustrated in FIG. 15, a composite reinforcement 90 having a shape of a truncated sphere is obtained.

The flexible abutment is made by forming a laminated structure alternating such composite armatures with layers of elastically deformable material (for example an elastomer). The stop may be made by stacking composite reinforcement of increasing size and interposing between each reinforcement a layer of elastically deformable material obtained by draping an unvulcanized elastomeric sheet. The number of reinforcements and layers of elastic material composing the flexible stop is determined according to the efforts to which the latter will have to resist. For example, a flexible abutment may comprise 7 frames with 6 layers of elastomeric material, each interposed between two successive frames. The set of composite reinforcements / layers of elastomeric material is then subjected to a thermal cycle (eg in an oven at 150 ^° C.) in order to vulcanize the elastomer composing the layers of elastic material.

According to a particular embodiment of a flexible abutment, a series (for example 7) of nested fibrous reinforcements (L 1 of increasing or decreasing size) is produced according to the method described above. Reinforcements are maintained in each other with metal spacers between each reinforcement corresponding to the thickness of the layers of elastically deformable material. The resin is injected and polymerized in all the reinforcements according to the RTM method. We remove tabs and place the frames on molds to maintain a space between each frame. The elastomeric material is then injected into the spaces formed between the reinforcements.

The wires 64 forming inter-layer connections in each armature (FIG. 15) make it possible to establish a thermal conductivity between two armatures, which facilitates the supply of heat in the layer of elastically deformable material between two armatures. In the case for example of elastic layers made of rubber, the presence of son 64 by increasing the thermal conductivity between the reinforcements improves the vulcanization thereof.

The fibrous layer production method of the present invention is obviously not limited to the sole fabrication of reinforcement as previously described. It can be used for the manufacture of any type of piece having a shape of revolution and whose surface is not developable.

Figure 16 shows another implementation of the method of the invention for the manufacture of an annular piece such as a housing. In this implementation, the fibrous layer consists of several series of fibers 122a and 122b, for example glass or carbon fibers, which are respectively placed in two different orientations corresponding to the directions of the mechanical forces (eg tension and compression) to which the part must be subjected. This placement of fibers in two orientations makes it possible to give the resulting part resistance to mechanical stresses with different directions.

As explained above, the fibrous layer is made from two canvases 120 and 121 defining an annular space 123. The canvases 120 and 121 delimit respectively the inner and outer periphery of the annular space whose width is chosen slightly greater than the necessary dimensions for the stratum.

Fibers 122a and 122b are arranged using TFP placement technology, i.e. by programming the automatic embroidery machine to place and couse the fibers 122a and 122b on the scrims respectively at an angle α and an angle -α (Figure 16). The angles α and -α can correspond for example respectively to + 45 ° and -45 °. The implementation of the automatic embroidery machine is the same as that described in connection with Figure 3, the placement and sewing of the fibers at angles α and -α are programmed in the numerical control of the machine.

Specifically, as shown in Figure 17A, the machine has for example in the annular space 123 a first series of fibers 122a at the angle α. As with the fibrous layer 30 described above, the gaps between the fibers 122a can be filled by placing additional fibers 123a in these spaces with the embroidery machine (FIG. 17B), the machine attaching these additional fibers to the adjacent fibers by stitching. The fiber content is then substantially constant at all points. As illustrated in FIG. 18A, the embroidery machine then has a series of fibers 122b at the angle -α on the series of fibers 122a and 123a. Additional fibers 123b are then added to fill the gaps between the fibers 122b (Fig. 18B).

These steps are optionally repeated to form several series of superimposed fibers arranged respectively according to the angle -α and o. After having made a circular seam 131 in the vicinity of the inner periphery of the annular space and cut the portion between the two scrims, then a fibrous layer 130 (FIG. 19) is obtained, the fibers 132 of which are held together by the seam circular 131 while maintaining a high flexibility, which allows to position easily on a tool or in a mold having a form of revolution and non-developable surface.

The fibrous reinforcement of the part to be produced may consist of a single layer 130 or a stack of several of these layers, each made from two scrims as previously described. In the case of a stack, the fibrous layers 130 may be bonded together by a wire passing through the layers in the direction of their thickness (Z direction) as for the bond made between the layers 30 and 50 in FIG. In a particular aspect of the invention, it is possible to form fibrous layers having thicker areas forming local reinforcements in the final piece. FIG. 20 shows a fibrous stratum 230 comprising a fibrous stratum 231 formed of two series of fibers respectively oriented at angles α and -α as previously described. The fibrous layer 231 further comprises a portion 232 made by repeated superposition of stitched fibers. The portion 232 is made by programming the automatic embroidery machine to repeat in a given area the placement and sewing of fibers thereby creating one or more thicker portions on the fibrous layer. Fibrous strata are thus obtained, locally comprising one or more thickening portions making it possible to manufacture parts of revolution comprising reinforced parts.

Once the fibrous reinforcement has been formed from one or more fibrous layers 130 and possibly comprising reinforcement portions 232, the part is molded by impregnating the reinforcement with a thermosetting resin which is polymerized by heat treatment. As for the manufacture of the flexible abutment reinforcement described above, the well-known RTM ("Resin Transfer Molding") transfer molding process is used. According to this method, the fiber reinforcement is placed in a metal mold preferably and then a thermosetting resin is pressurized under pressure. Resin can be, for example, a cyanate ester temperature class resin

250 ⁰ C (maximum temperature supported by the resin without loss of characteristics). Suitable resins for the RTM process are well known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of the temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the piece must be subjected. Once the resin is injected into the entire reinforcement, it is polymerized by heat treatment in accordance with the RTM method. After injection and polymerization, the part is demolded. It can possibly undergo a post-baking cycle to improve its thermomechanical characteristics (increase of the glass transition temperature). In the end, the piece is cut away to remove the excess resin and the chamfers are machined. No other machining is necessary since, the part being molded, it respects the required dimensions.

Claims

1. A method of producing a fibrous stratum (30) intended to form a preform of a composite part of revolution and a non-developable surface, characterized in that it comprises the steps of:

- defining an annular space (23) with a first and a second scrim (20, 21) delimiting respectively an inner periphery and an outer periphery, - arranging the fibers (22) between the scrims (20, 21) by placing the fibers in the annular space in at least one direction and holding said fibers on the canvas by sewing,

- Making a circular seam connection (31) in the vicinity of the inner periphery of the annular space (23), and - Cut the fibrous layer (30) thus formed in the annular space (23) to extract it from the canvas .

2. Method according to claim 1, characterized in that additional fibers (27) are added to fill the free spaces present between the fibers (20) arranged between the two scrims (20, 21), the fibers being fixed to the adjacent fibers by sewing.

3. Method according to claim 1 or 2, characterized in that the fibers (20, 27) are carbon fibers or glass fibers.

4. Method according to any one of claims 1 to 3, characterized in that the fibers (20, 27) are arranged and sewn by an automatic embroidery machine.

5. A method of manufacturing a fibrous reinforcement (80) for flexible stop composite reinforcement comprising the formation of a preform alternating at least two fibrous layers (30, 50), characterized in that the first layer (30) is produced in accordance with method according to any one of claims 1 to 4, and that the second layer (50) is formed by placing on the first layer, maintained in shape on a spherical tool (40), a stratum of fibers oriented perpendicular to the fibers of the first stratum.

6. Method according to claim 5, characterized in that the second layer (50) is made by filamentary winding on the first layer (30).

7. Method according to claim 5 or 6, characterized in that the strata (30, 50) of the fibrous reinforcement (80) are interconnected by son (64).

8. A method of manufacturing a flexible abutment reinforcement characterized in that it comprises the manufacture of a fibrous reinforcement (80) according to the method according to any one of claims 5 to 7 and that the fibrous reinforcement ( 80) is placed in a mold (70) in which is injected under pressure a thermosetting resin (71), the polymerization of the resin is then carried out by heat treatment.

9. Process according to claim 8, characterized in that the resin

(71) is an epoxy resin.

10. A method of manufacturing a flexible stop formed of a laminated structure comprising a plurality of rigid reinforcement interposed with layers of elastically deformable material, characterized in that each reinforcement is produced according to the method according to claim 8 or 9.

11. A method according to claim 10, characterized in that the layers of elastic material are composed of elastomer or rubber and in that the laminated structure is subjected to a heat treatment to vulcanize the elastomer or rubber.

12. A method of manufacturing a flexible abutment formed of a laminated structure comprising a plurality of rigid reinforcements interposed with layers of elastically deformable material characterized in that it comprises the steps of:

- producing a plurality of fibrous reinforcements (80) of increasing size according to the method according to any one of claims 5 to 7,

- Maintaining reinforcements in each other with spacers between each armature, said spacers defining the thickness of the layers of elastically deformable material,

injecting under pressure into the reinforcements a thermosetting resin,

applying a heat treatment to polymerize the resin in each reinforcement so as to form a plurality of rigid composite reinforcements,

- Remove the spacers, and - inject or sink an elastic material in the spaces between the rigid composite reinforcement to form layers of elastic material between them.

13. The method of claim 10, characterized in that the layers of elastic material are composed of elastomer and in that the laminated structure is subjected to a heat treatment to vulcanize the elastomer.

14. A method of manufacturing a composite part of the housing type comprising the formation of a fibrous reinforcement composed of at least one fibrous layer (130) characterized in that said layer is made according to the process according to any one of the claims. 1 to 4 and in that it is formed of fibers (122a, 122b) oriented in two different directions.

15. The method of claim 14, characterized in that one or more thickening portions (232) are formed at predetermined locations on each fibrous stratum (231), said portions being made by repeating the placement of fibers at predetermined locations. on the stratum.

16. The method of claim 14 or 15, characterized in that the reinforcement is placed in a mold in which is injected a thermosetting resin, the polymerization of the resin is then carried out by heat treatment.

17. The method of claim 16, characterized in that the resin is a cyanate ester resin.